Ethane Generation Research Articles

Studies into the Action of Some Photosynthetic Inhibitor Herbicides

Treatment of flax cotyledons with solutions of bromacil, ioxynil, metribuzin, and monuron resulted in a rapid inhibition of CO2 fixation. Chloroplasts isolated from cotyledons treated with the above herbicides exhibited electron transport activity for some time after CO2 uptake in the intact cotyledons had ceased. However, the action of the herbicides was to decrease photosystem two (PSII) activity faster than photosystem one (PSI) activity but there appeared to be no differential breakdown of the pigment complexes resolved by polyacrylamide gel electrophoresis. Carotenoid breakdown, particularly α- and β- carotene, preceded chlorophyll loss following herbicide treatment. Ethane generation, an indicator of membrane breakdown, increased as the pigment levels decreased. Incubation of cotyledons in an argon atmosphere reduced the rate of pigment loss with ioxynil treatment and prevented pigment breakdown with monuron treatment. Pigment loss was also reduced by the addition of a singlet oxygen quencher, l, 4-diazo-bicyclo(2, 2, 2)octane (DABCO). Ultrastructural effects commenced with a rapid swelling of the chloroplast followed by a gradual disorganization and swelling of the thylakoid system and subsequent tonoplast rupture. With ioxynil numerous membrane-bound vesicles were formed in the chloroplast prior to envelope rupture. The evidence suggests that, following inhibition of electron transport, the photosynthetic inhibitor herbicides exert their toxic effect by causing the formation of excited singlet oxygen. It is suggested that this is initially quenched by the chloroplast protective mechanisms; however, since these systems are overloaded subsequent membrane breakdown occurs.

Generation and migration of light hydrocarbons (C 2C 7) in sedimentary basins

Sixty-five samples from selected source bed-type shale sequences from three exploration wells were analysed for yield and detailed composition of light hydrocarbons(C 2C 7) by a new hydrogen stripping/capillary gas chromatographic technique. In spite of low maturation levels (0.35–0.55% vitrinite reflectance), significant generation of ethane and propane was recognized in a Jurassic source bed sequence bearing hydrogen-poor kerogens. Light hydrocarbon generation in another and mature Jurassic source rock sequence is controlled by kerogen quality. Associated with a change from hydrogen-poor to hydrogen-rich kerogens, yields of total and most individual hydrocarbons exhibit orders-of-magnitude increases. At the same time, iso/n-alkane ratios for butanes, pentanes and heptanes decrease significantly. A study of an interbedded marine/nonmarine coal-bearing sequence of Upper Carboniferous age from the Ruhr area, West Germany, revealed that a marine shale unit in comparison to the adjacent coal seam is more prolific in generating n-alkanes of increasing molecular size. A case history for migration of light hydrocarbons by means of diffusion through shales is presented. In two shallow core holes in Campanian/Maastrichtian shales in West Greenland, upward diffusion of ethane to pentane range hydrocarbons is an active process within the near-surface 3 m interval. Diffusive losses within this interval amount to 99.8% for propane, 85.6% for n-butane and 38.9% for n-pentane.

The Role of Light and Oxygen in the Action of the Photosynthetic Inhibitor Herbicide Monuron

Abstract Monuron treatment of detached flax cotyledons caused a rapid inhibition of CO2 fixation in darkness and light. Chlorophyll breakdown was promoted by increased light intensity. Ethane generation, an indicator of membrane damage, increased as the chlorophyll level decreased. The carotene pigments were destroyed more rapidly than the xanthophylls and chlorophylls. Treatment of cotyledons with monuron in the absence of oxygen almost prevented carotenoid and chlorophyll loss. The addition of the singlet oxygen quencher DABCO delayed chlorophyll breakdown. The results are discussed in relation to a role for singlet oxygen in the herbicidal action of monuron.